ANSI Common Lisp 4 Types and Classes 4.3 Classes 4.3.6 Redefining Classes
188.8.131.52 Customizing Class Redefinition
Methods for update-instance-for-redefined-class may be
defined to specify actions to be taken when an instance is updated.
If only after methods for update-instance-for-redefined-class are
defined, they will be run after the system-supplied primary method for
initialization and therefore will not interfere with the default
behavior of update-instance-for-redefined-class. Because no
initialization arguments are passed to update-instance-for-redefined-class
when it is called by the system, the
initialization forms for slots
that are filled by before methods for update-instance-for-redefined-class
will not be evaluated by shared-initialize.
Methods for shared-initialize may be defined to customize
class redefinition. For more information, see Section 7.1.5 Shared-Initialize.